1. Field of the Invention
The present invention relates to a drag reduction surface and method whereby skin friction drag caused by wall surface bounded turbulent shear flows is reduced. In particular, the present invention relates to the use of rearward facing microsteps with and without intermittent phased tangential blowing to reduce the drag.
2. Prior Art
The prior art has shown the use of riblets in the surface and lebus (raised air foils across the flow) in the outer region of the boundary layer to be effective in reducing drag. Such devices are described in Walsh, M. J., AIAA 20th Aerospace Sciences Meeting, AIAA-82-0169, NASA Langley Research Center, Hampton, Va., Jan. 11-14, 1982; Bechert, D. W., et al, Short report on measurements with sawtooth riblets (3M plastic riblet film), DFVLR, Mueller-Breslau-Str. 8, 1000 Berlin-West 12, F.R.G. (1988); and Walsh, Michael J., et al. AIAA 6th Applied Aerodynamics Conference, AIAA-88-2554, NASA Langley Research Center, Hampton, -Virginia Jun. 6-8, 1988), and U.S. Pat. No. 4,706,910 to Walsh et al. U.S. Pat. No. 4,664,345 to Lurz shows the use of a single step. This patent does not provide the steps in an organized manner to control the surface bounded turbulent shear flows of a fluid. These surface modification devices are effective and can be used in the present invention.
Steps have been used for many years on boats and the like to reduce drag. These steps have heights which are well beyond the sublayer region adjacent to the wall surface.